Production of ultra-thin nano-scaled graphene platelets from meso-carbon micro-beads

Abstract

A method of producing nano-scaled graphene platelets (NGPs) having an average thickness no greater than 50 nm, typically less than 2 nm, and, in many cases, no greater than 1 nm. The method comprises (a) intercalating a supply of meso-carbon microbeads (MCMBs) to produce intercalated MCMBs; and (b) exfoliating the intercalated MCMBs at a temperature and a pressure for a sufficient period of time to produce the desired NGPs. Optionally, the exfoliated product may be subjected to a mechanical shearing treatment, such as air milling, air jet milling, ball milling, pressurized fluid milling, rotating-blade grinding, or ultrasonicating. The NGPs are excellent reinforcement fillers for a range of matrix materials to produce nanocomposites. Nano-scaled graphene platelets are much lower-cost alternatives to carbon nano-tubes or carbon nano-fibers.

The invention claimed is: 
     
       1. A method of producing separated nano-scaled graphene platelets having a thickness less than 3 nm, said method consisting of:
 a) intercalating a supply of meso-carbon microbeads (MCMBs) to produce intercalated MCMBs; and 
 b) exfoliating said intercalated MCMBs at a temperature and a pressure for a sufficient period of time to produce said nano-scaled graphene platelets. 
 
     
     
       2. The method of  claim 1  wherein said graphene platelets have a thickness less than 1 nm. 
     
     
       3. The method of  claim 1  wherein said graphene platelets comprise single graphene sheets, double-layer graphene sheets, or triple-layer graphene sheets. 
     
     
       4. The method of  claim 1  wherein said graphene platelets have a length less than 100 nM. 
     
     
       5. The method of  claim 1  wherein said supply of MCMBs is obtained from a petroleum heavy oil or pitch, coal tar pitch, polynuclear hydrocarbon, or a combination thereof. 
     
     
       6. The method of  claim 1  wherein said supply of MCMBs is treated at a temperature in the range of 500° C. and 3,000° C. 
     
     
       7. The method of  claim 1  wherein said supply of MCMBs is obtained from heat-treating mesophase carbon spheres at a temperature in the range of 500° C. and 1,400° C. and said graphene platelets have a length smaller than 10 nm. 
     
     
       8. The method of  claim 1  wherein said supply of MCMBs is obtained from heat-treating mesophase carbon spheres at a temperature higher than 2,500° C. and said graphene platelets have a length greater than 350 nm. 
     
     
       9. The method of  claim 1  wherein said step of intercalation includes intercalating an intercalate into said supply of meso-carbon microbeads wherein said intercalate is selected from an acid, an oxidizing agent, a mixture of an acid and an oxidizing agent, a halogen molecule or inter-halogen compound, a metal-halogen compound, an alkali metal, a mixture or eutectic of two alkali metals, an alkaline earth metal, an alkali metal-organic solvent mixture, or a combination thereof. 
     
     
       10. The method of  claim 1  wherein said step of intercalation comprises intercalating an intercalate into said supply of meso-carbon microbeads wherein said intercalate is selected from acetic acid, formic acid, or a carboxylic acid. 
     
     
       11. The method of  claim 10  wherein said carboxylic acid is selected from the group consisting of aromatic carboxylic acid, aliphatic or cycloaliphatic carboxylic acid, straight chain or branched chain carboxylic acid, saturated and unsaturated monocarboxylic acids, dicarboxylic acids and polycarboxylic acids that have 1-10 carbon atoms, alkyl esters thereof, and combinations thereof. 
     
     
       12. The method of  claim 1  wherein said step of intercalating comprises chemical intercalating, electrochemical intercalating, gaseous phase intercalating, liquid phase intercalating, supercritical fluid intercalating, or a combination thereof. 
     
     
       13. The method of  claim 12  wherein said electrochemical intercalating comprises intercalating a carboxylic acid into the MCMBs by imposing a current between said MCMBs and a metal or graphite material for a duration of time sufficient for producing the interacted MCMBs. 
     
     
       14. The method of  claim 13  wherein said current imposed to said supply of MCMBs is at a current density in the range of 50 to 600 A/m 2 . 
     
     
       15. The method of  claim 1  wherein said step of intercalating is completed in 30 minutes or less. 
     
     
       16. The method of  claim 1  wherein said step of intercalating is completed in 15 minutes or less. 
     
     
       17. The method of  claim 1  wherein said step of exfoliating said intercalated MCMBs comprises exposing said intercalated MCMBs to a temperature in the range of 150° C. to 1,100° C. 
     
     
       18. The method of  claim 1  wherein said step of intercalation comprises intercalating an acid into said MCMBs and said step of exfoliating said intercalated MCMBs comprises exposing said intercalated MCMBs to a temperature in the range of 150° C. to 300° C. 
     
     
       19. The method of  claim 1  further comprising a step of contacting at least a part of the exfoliated MCMBs with a liquid selected from water, methanol, ethanol, acetone, an organic solvent, or a combination thereof. 
     
     
       20. The method of  claim 1  wherein said step of intercalation consists of exposing said MCMBs to a gaseous or supercritical fluid environment at a first temperature and a first pressure and said step of exfoliation comprises subjecting said intercalated MCMBs to a second temperature and a second pressure, wherein said first temperature is different from said second temperature or said first pressure is different from said second pressure. 
     
     
       21. The method of  claim 20  wherein said gaseous or supercritical fluid environment comprises carbon dioxide.